Lectins, protein that bind carbohydrates, have been implicated as major determinants in rhizobia-legume recognition. Lectins are also known to be involved in other biologically important examples of cell-cell recognition. The major goal of this research is to elucidate the molecular mechanism of host recognition in the Bardyrhizobium japonicum-soybean symbiosis. It is hoped that this research will add to the general knowledge of the mechanism of specific cell-cell recognition and the role of lectins in such recognition. Recent results suggest a model by which lectin interaction with B. japonicum induces changes in the cell wall polysaccharides. These and other changes may define the role of lectin in the infection mechanism. Therefore, our research will focus on these changes with special emphasis on the cell surface polysaccharides. In conjunction with this, we will investigate the role of the outer membrane in the infection mechanisms. The outer membrane of B. japonicum appears to undergo modification early in the infection cycle. All of the above cell surface changes may be critical to the determination of host specificity.